In Aumann's agreement theorem the two rationalists have common knowledge of the subject and share common priors. These two conditions are not true in the common cases you are discussing. Two rationalists can agree that it is not worth while to take the time to make all pertinent knowledge common and come to common priors. This can only happen with unimportant topics because otherwise it would be worth spending more time on it, this is still not agreeing to disagree.
Only their posteriors need to be "common knowledge" - which is pretty weak - and seems worlds away from making "all pertinent knowledge common". See page 1 here for details.
For a nice expression of the idea, see here:
Imagine I think there are 200 balls in the urn, but Robin Hanson thinks there are 300 balls in the urn. Once Robin tells me his estimate, and I tell him mine, we should converge upon a common opinion. In essence his opinion serves as a "sufficient statistic" for all of his evidence.
http://www.marginalrevolution.com/marginalrevolution/2005/10/robert_aumann_n.html
In particular the bit: "In essence his opinion serves as a 'sufficient statistic' for all of his evidence".
This is usually considered to mean that sharing the information required to produce convergence is usually a rather small effort - since relatively few bits of opinion need to be passed back and forth - rather than lots of facts and evidence.
I was not using the term "common knowledge" the same way Aumann paper was. I was baseing my use of the term on what I found in the lesswrong wiki. I used common knowledge and common priors as essentially the same object in my post. Having the same priors seems to require "all pertinent knowledge" be known by both parties or known in common(this is how I used the term in my post) or a large coincidence where two, pertinent, partial non-overlapping(at least), lead to the same priors.
...Imagine I think there are 200 balls in the urn, but R
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